Air separator for extracorporeal fluid treatment sets

ABSTRACT

An air separator ( 1 ) comprises a first chamber ( 2 ) where blood or other fluid can be received, an inlet and an outlet port associated to the bottom wall ( 4 ) and in fluid communication with the first chamber. A first channel ( 14 ) extending along the lateral wall of the separator and has a first and a second portion ( 16  and  18 ). The channel second portion ( 18 ) terminally forms an orifice ( 15 ) facing the chamber and extending in an area closer to a top wall ( 5 ) of the chamber ( 2 ) than to the bottom wall of the same chamber. The orifice faces the top of the separator and has a flow passage cross section greater than that of a first portion ( 16 ) of the channel.

FIELD OF THE INVENTION

The invention relates to an air separator for extracorporeal fluidtreatment set. The air separator of the invention can for instance beused in extracorporeal blood treatment procedures, or in proceduresinvolving extracorporeal displacement of blood or of blood components orof medical fluids.

BACKGROUND OF THE INVENTION

By way of non-limiting example and in order to provide a background tothe present invention reference is made to the field of extracorporealblood treatment.

As it is well known in the art, blood treatment apparatus, such ashemodialysis machines, are used to continuously remove impurities from apatient's blood. The blood is typically pumped through tubes and movedthrough arterial and/or venous bubble traps (air separators) associatedto disposable tubing sets connecting the patient to a dialyzer or othertreatment unit mounted on the hemodialysis machine.

U.S. Pat. No. 4,263,808 discloses a one-piece hydraulic circuit thatincludes arterial and venous bubble trap chambers in which blood entersat entrances above the bottoms of the chambers and leaves near thebottoms of the chambers. Pressure in the chambers can be determined bytransducers placed against impermeable latex membranes covering holescommunicating with upper portions of the chambers.

U.S. Pat. No. 4,666,598 discloses a fluid flow chamber cassette that canbe mounted with either its front wall or rear wall against a supportingmachine, such as a hemodialysis machine, and has a flexible tube thatextends from a sidewall and forms a loop that is symmetrical about aloop axis that is transverse to the side wall so that the loop will beacted upon by a pump roller on the machine both when the front wall isagainst the machine and when the rear wall is against the machine. Theorientation of the cassette and the direction of fluid flow through thecassette can thus be changed by simply changing whether the front or therear wall is mounted against the machine. The cassette comprises anarterial chamber and a venous chamber. The arterial chamber inlet entersthe arterial chamber at a position higher than the arterial chamberoutlet, and the venous chamber inlet enter the venous chamber at aposition higher than the venous chamber outlet. When priming by causingreverse flow, the liquid rises in the venous and arterial chambers tothe levels of the entrances of the inlets, and the amount of air in thechambers remains fixed, even after flow is reversed during normaloperation with blood. Each of the arterial and venous chambers has acorresponding impermeable flexible diaphragm over a hole in a rigid wallof the chamber for the purpose of sensing pressure.

So-called “bottom entry” chambers whereby the blood inlet port is at thebottom of the chamber and blood enters into the blood space at thebottom or sidewall of the chamber are known from U.S. Pat. No.4,681,606, U.S. Pat. No. 4,668,598 and European Patent No. 0058325.

Finally, U.S. Pat. No. 5,605,540 discloses a one-piece, plastic, blowmolded arterial or arterial-venous blood chamber with bottom entryhaving equal height inlet and outlet wherein both the inlet and outlethave a progressively increasing cross section when moving from thebottom to the top of the chamber.

Furthermore the applicant has in the past put on the market airseparators as schematically shown in appended FIGS. 7A and 8A.

SUMMARY OF THE INVENTION

The applicant has found that the structure of the blood or medical fluidchambers could be further improved in order to:

-   -   enhance air separation, and avoid that air bubbles undesirably        reach the chamber outlet,    -   minimize foam formation in correspondence of the blood inlet,        which could lead to problems in efficient air separation, and    -   reduce stagnation areas which could contribute to formation of        clots.

The above aims are reached by an air separator according to the appendedclaims.

According an aspect of the present invention the orifice bringing bloodor other fluid into the chamber of the air separator is relativelydistant from the outlet port.

According to a further feature of the invention the orifice is orientedso as to direct the liquid towards the top of the blood chamber.

These provision leave time to flow deceleration allowing the bubbles toseparate from blood before this latter reaches the outlet port.

A further aspect of the invention provides for an inlet (first) channelwhere flow speed is significantly reduced and flow stability increasedusing two or more consecutive portions of progressively increasing crosssection. This results in a substantial reduction of foam formation andcontributes to the separation of any air bubbles present in the incomingblood.

In accordance with another aspect of the invention the air separatorpresents a filter inside the chamber and the orifice is placed farenough from the area of interest of the filter, as it is desirable thatbubbles are separated before reaching any zone where they could betrapped and then uncontrollably released to the patient. Moreover if thefilter is positioned and extends in correspondence of an areasufficiently far from the inlet channel orifice, stagnation areas incorrespondence of the filter surface are less probable.

Further characteristics and advantages will better emerge from thefollowing description in relation to some preferred but non-exclusiveembodiments of an air separator according to the invention.

SHORT DESCRIPTION OF THE DRAWINGS

The description will be made with reference to the figures of theaccompanying drawings, provided by way of non-limiting example, inwhich:

FIG. 1 is a front elevation of an air separator according to theinvention;

FIGS. 2 and 3 are side views of the separator of FIG. 1;

FIGS. 4 and 5 are top and bottom views of the separator of FIG. 1;

FIG. 6 is a section of the separator of FIG. 1;

FIGS. 7A and 7B are schematic elevation views showing blood in a bloodchamber of known design and in an air separator according to theinvention respectively;

FIGS. 8A and 8B are schematic elevation views showing the flow speedpattern of blood in a blood chamber of known design and in an airseparator according to the invention respectively.

FIGS. 9 and 10 are schematic elevation views showing a separatoraccording to possible alternative embodiments of the invention;

FIG. 11 is an elevation view showing a blood circuit where the airseparator of FIG. 1 could be used.

FIG. 12 is a schematic of an extracorporeal blood circuit adopting theair separator of the present invention.

DETAILED DESCRIPTION

Referring to the enclosed drawings, several non-limiting embodiment ofan air separator 1 according to the invention are shown. By way ofnon-limiting example the detailed description will make reference to ause of the air separator for separating air bubbles from blood, as it isthe case when the separator 1 is used in extracorporeal blood treatmentsets. The air separator comprises a first and a second chamber 2 and 3(see FIG. 6) positioned in side by side relationship with respect toeach other. Of course, depending upon the circumstances, the airseparator could comprise only the first chamber. The first chamberpresents a respective bottom wall 4, a respective top wall 5, and arespective lateral wall 6 extending between the top and bottom walls 4and 5. Similarly the second chamber has a respective bottom wall 7, arespective top wall 8, and a respective lateral wall 9 extending betweenthe top and bottom walls 7 and 8. The lateral wall of the embodimentsshown in the attached drawings is formed by flat portions: it is howeverto be understood that the lateral wall could be curved. Also the shapeof the top and bottom walls is not limited to the specific shape shownin the attached drawings.

The bottom wall of each chamber is provided with respective inlet andoutlet ports for the fluid coming in the chamber and going out of thechamber. For sake of clarity the inlet and outlet ports 10 and 11 of thefirst chamber 2 are herein referred to as first inlet port 10 and firstoutlet port 11, while the inlet and outlet ports of the second chamberare herein referred to as second inlet port 12 and second outlet port13.

In all embodiments shown in the attached drawings, the air separatorcomprises a first channel 14 extending parallel to at least a portion 6a of the lateral wall 6 of the first chamber 2 and having a first end 14a, connected to the first inlet port 10, and a second end 14 b,terminating into the first chamber in a position closer to said top wall5 that to said bottom wall 4; the portion 6 a is an inferior side partof the lateral wall. The second end 14 b of the first channel 14terminally delimits an orifice 15 which opens into the chamber and facessaid top wall. Referring to a working condition, the plane of FIG. 1represents a vertical plane and therefore the first channel developsvertically and the terminal orifice is substantially horizontal andfaces the top of the air separator.

In all embodiments, the first channel has a first portion 16, directlyconnected to the first inlet port 10, and a second consecutive portion18, defining a flow passage cross section greater then that of the firstportion. Notice that 3 or more consecutive portions could be envisaged:in such a case too the cross section of the portions would increasemoving away from the inlet port 10.

With the definition ‘flow passage cross section’ it is herein meant thenet area available for fluid flow passage in correspondence of a certainsection of a fluid channel or fluid chamber.

Fluid flowing into the first inlet port moves through the firstrelatively narrow portion and then through the second relatively largeportion so that fluid speed is proportionally reduced when passing fromthe first to the second portion before entering the chamber 2.

In the embodiment of FIGS. 1-6 and in the embodiment of FIG. 10 thefirst flow passage cross section and the second flow passage crosssection are constant so as to define two tubular portions where the netarea for the passage of fluid is constant and therefore flow speed canstabilize. FIG. 10 alternative embodiment has one chamber only: i.e. thefirst chamber. Notice however that the first chamber of FIG. 10 could beassociated to a second chamber in a way similar to the embodiment ofFIGS. 1-6.

For a better understanding of the geometry of the air separatorsaccording to the invention and referring to non-limiting examples ofFIGS. 6, 9 and 10, the following definitions are given:

-   -   D1 represents the measure of the distance between the top wall 5        inner surface and the bottom wall 4 inner surface (in some cases        the top and/or the bottom wall could not be flat and parallel:        in such cases D1 is the distance between the lowermost region of        the bottom wall and the uppermost region of the top),    -   D2 represents the measure of the distance between the horizontal        plane where the orifice 15 of the first channel extends and the        bottom wall (in some cases the bottom wall could not be flat and        parallel to the horizontal: in such cases D1 is the distance        between the horizontal plane containing the orifice and the        lowermost region of the bottom),    -   A1 represents the measure of the flow passage cross section area        of the first channel 14 in correspondence of said orifice        (referring to the enclosed examples A1 is measured taking a        horizontal section in correspondence of the orifice),    -   A2 represents the measure of the flow passage cross section area        of the first chamber in correspondence of said orifice        (referring to the enclosed examples A2 is measured taking a        horizontal section of the first chamber at the same vertical        position of the orifice),    -   A3 represents the measure of the flow passage cross section area        of the first channel in correspondence of the first portion 16        (referring to the enclosed examples A3 is measured taking a        horizontal section in correspondence first portion).

In the embodiment of FIGS. 1-6, the first channel comprises a connectionportion 17 consecutively connecting the second portion to the firstportion and having a progressively increasing flow passage crosssection. In practice the connection portion can be obtained by a wallportion inclined with respect to the direction of longitudinaldevelopment of each portion 16 and 18. In FIG. 10 embodiment, the twoconsecutive portions 16 and 18 are placed one downstream the other andan aperture in correspondence of the area of connection of the twoportions. This aperture, together with the above mentioned orifice 15,serves to put the channel 14 into communication with the chamber andgives a preferential path for fluid coming from the inlet port 10 andnot having enough kinetic energy to reach the orifice 15. In theembodiments of FIGS. 1-6 and 10, A1 is between 1.5 and 2.5 times A3.

FIG. 9 shows an alternative embodiment where the air separator 1 has onechamber only: i.e. the first chamber. Notice however that the firstchamber of the embodiment shown in FIG. 9 could be associated to asecond chamber in a way similar to the embodiment of FIGS. 1-6. In theembodiment of FIG. 9, the channel 14 presents a second portion 18 wherethe flow passage cross section increases in a progressive and continuousmanner moving towards said second end (i.e. with reference to theattached figures the net area for the fluid passage increases movingcloser to the top wall). According to a possible variant of theembodiment of FIG. 9, the channel 14 can present a continuously andprogressively increasing flow passage cross section from said first tosaid second end.

Also in the embodiments of FIG. 9, A1 is between 1.5 and 2.5 times themeasure of A3.

Returning to a description of features common to all embodiments, thefirst channel 14 has a longitudinal extension parallel to the lateralwall of the first chamber such that the orifice results to be positionedin a certain position relative to said top and said bottom walls. Usingthe above definitions D2/D1 is greater than 0.5 and for instancecomprised between 0.55 and 0.7.

Moreover, the ratio A1/A2 is greater than 0.25, meaning that the fluiddoes not abruptly pass from a narrow channel into a large chamber butrather the flow passage cross section area of the first channel incorrespondence of the orifice is at least ¼ (in the shown embodimentsaround ⅓) the flow passage cross section area of the first chamber incorrespondence of the orifice (i.e. the area of the fluid passage in thefirst chamber measured at the same height of the orifice as shown inFIG. 9, see references A1 and A2). The ratio A1/A2 as above defined ishas also an upper limit in that it is less then 1.00 and preferably lessthan 0.75, meaning that the orifice area is preferably smaller than thearea of the first chamber in correspondence of the same section of theair separator.

The air separator can also comprise a filter 19 engaged to the bottomwall in correspondence of the outlet port 11 and axially extending intothe chamber according to a direction substantially parallel to the firstportion of the channel. The filter can have a substantially cylindricalor frusto-conical or conical overall shape and meshes designed dependingupon the needs.

The filter extends axially into the chamber from the bottom wall 4lowermost region 4 a and presents an overall axial extension into thefirst chamber (which is identified as D3 in the attached drawings)sensibly less than D2. According to the embodiment of FIG. 1, the filterpresents an overall axial extension D3 substantially not greater than0.70 of D3. In the embodiments shown, the axial length of the filter isless then that of the first portion 16 of the first channel 14 so thatthe filter 19 remains sufficiently distant from the first channelorifice 15.

The air separator can also comprise a second channel 20 (as for instancein the embodiment of FIGS. 1-6) extending parallel to the lateral wallof the second chamber 3 and having a first end 20 a, connected to thesecond inlet port 12, and a second end 20 b terminating into the secondchamber; the second channel has constant cross section and presents adeflector 21 in correspondence of its second end defining an orifice 22facing the lateral wall 9 of the second chamber. In practice flow comingfrom the second inlet moves through the second channel and (withreference to use conditions) turns substantially by 90°, therebyhorizontally entering into the second chamber.

The orifice 22 faces the lateral wall 9 and extends across an area whichis below the horizontal plane where the orifice 15 of the first channellies (again with reference to a use condition of the separator).

Under a structural perspective, the overall air separator of the shownembodiments has a flattened configuration where said first channel andsaid first chamber have a substantially square shaped transversesection. The separator can be made in rigid and transparent plasticmaterial. By way of non limiting example one of the following plasticmaterials could be used: PETG, PVC; however, any other suitable materialcould be of course equivalently used without departing from the scope ofthe invention which is directed to the geometry of the separator ratherthen to the specific materials used for the manufacture.

For instance the following materials could represent alternative choicesfor the separator manufacturing: Copolyester (e.g. Eastar copolyesterPETG from Eastman Chemical Company), Acrylic-based multipolymercompounds (e.g. Cyrolite® trademark of Cyro Industries),Styrene-Butadiene block copolymer (S/B/S) (e.g. Styrolux® from BASF),MABS (e.g. Terlux® from BASF), Styrene-Methyl-Methacrylate-Butadienepolymers (e.g. Zylar® or NAS® from Nova Chemicals).

The entire air separator is made can be in one single piece, forinstance by injection molding. In particular, the first channel 14 andthe first chamber walls 4,5,6 are in one single plastic piece where thechannel 14 presents a lateral wall having a longitudinal portion incommon with a portion of the first chamber lateral wall. Similarly, whenpresent, the second blood chamber can be in one piece with the firstblood chamber and integrally bears the second channel 20.

In the embodiment of FIG. 6, each one of the first and second bloodchambers presents a lateral wall formed by a front wall, a rear wallspaced from the front wall, side walls extending between said front andrear walls. The first and second chamber are joined in correspondence ofone common side wall 25 which extends in correspondence of a centralzone of the air separator; the front and rear walls of each chamber arecoplanar and cooperate to define the front and rear walls of the entireair separator. An intermediate wall 23 extends between the front andrear walls of each blood chamber and laterally delimits the respectivechannel in cooperation with one of said side walls. In FIG. 6, theintermediate wall 23 associated with the first blood chamber presents afirst wall portion 23 a parallel to one of the side walls, a second wallportion 23 b parallel to the same side wall and a deflecting portion 23c connecting said first and second portion thereby forming said firstand second portions 16 and 18 as well as portion 17. In FIG. 9 the wall23 presents a terminal curved portion defining the second portion 18 offirst channel 14. In FIG. 10 the intermediate wall 23 is defined by two(or more) wall portions 23 a and 23 b separated by an aperture 23 d.

The lateral wall of the first chamber can be designed to includepressure transducer means 24. In such a case the first channel endsimmediately below said pressure transducer means. Also the secondchamber can have respective pressure transducer means 24.

The pressure transducer means can include a hole on the air separatorwall and a respective diaphragm tightly occluding the hole. Thediaphragm is subject to deformation under the action of a pressuredifference between the inside and the outside of each respective chamberand transmits a corresponding pressure signal to a tube connected to apressure sensor inside the dialysis machine (or other treatmentmachine). U.S. Pat. No. 4,666,598 discloses in detail a possibleembodiment for the pressure transducer means of the type just described.The pressure transducer means could also be different from the abovedescribed solution: for instance the diaphragm could be integrally inthe obtained in the side wall by a thickness reduction in the wall whichdefines a movable part integral with the rest of the wall. According toa further alternative pressure could be detected via respective linesbringing the air to corresponding transducers remote from the airseparator. Still another alternative provides for pressure sensorsdirectly integrated on the separator wall and directly providing anelectric signal function of the pressure inside the separator(piezoelectric sensors could be used). However, the way pressure in theblood chambers is detected is however not relevant for the presentinvention and any alternative means could equivalently be adopted.

FIG. 11 discloses an extracorporeal blood circuit 60 wherein airseparator 1 of the type of FIGS. 1-6 is used.

The blood circuit 60 comprises an arterial line 70 which has at leastone end 71 designed to be connected to a patient and another end 72designed to be connected with a blood treatment unit, a venous line 73which has at least one end 74 designed to be connected to a patient andanother end 75 designed to be connected with a blood treatment unit.

The air separator of present invention is associated to the venous andarterial lines as here below described in details.

The venous line 73 includes a first flexible tube 79 having one endengaged to the inlet port 10 of the first blood chamber 2 and theopposite end 75 where a connector can be present. The venous line alsoincludes a second flexible tube 80 having one end engaged to the outletport 11 of the first blood chamber and the other end, which has alreadybeen identified with reference numeral 74, being for connection with apatient (via an access device not shown in the attached drawings). Thearterial line 70 includes a third flexible tube 81 engaged to the inletport 12 of the second blood chamber and terminating in correspondence ofsaid end 71. The arterial line also includes a fourth flexible tube 82engaged to the outlet port 13 of the second blood chamber and to onewall of said second blood chamber for forming a loop 83 which issymmetric about a loop axis transverse to the lateral wall of the secondchamber. In the embodiment of FIG. 4 the tube 82 connects the outletport 13 with a rigid channel 84 extending above the chambers 2 and 3which then leads to a fifth flexible tube 85 terminating incorrespondence of said end 72 where a connector can be present.

Of course depending upon the treatment the blood circuit could also beprovided with one or more infusion lines which can be branched to anyoneof tubes 79 and/or 80 and/or 81 and/or 85.

In use tubular extensions 86 engaging the tube 82 together with one ormore projections 87 are used to lock in operating position the airseparator to a treatment machine panel. Looped tube 82 fits around therollers of a peristaltic pump (not shown) carried on the front of themachine and liquid (blood or other liquid) can be pumped into the bloodcircuit. Of course depending upon the liquid to be pumped and upon theprocedure to be put in place, proper connections with the patient andwith the treatment unit have to be put in place as already well known inthe art.

The described tubing can be made in any plastic material suitable formedical use, such as Single layer tubing made from Plasticized PVC(DEHP, or DEHP-free alternatives as plasticizer); multi-layer tubingincluding an outer layer of Plasticized PVC (DEHP, or DEHP-freealternatives as plasticizer), or Chlorine-free polymeric materials (e.g.thermoplastic elastomer polyurethanes, SEBS or SEPS-based compounds) andcomprising an inner layer of polymeric material obtained from acombination of at least a polyolefin chosen in the group formed bypolyethylene or polypropylene and at least one elastomer chosen in thegroup formed by SEPS or SEBS.

FIG. 12 schematically shows the fluids flow circuit defined by the bloodcircuit and the air separator of FIG. 11 when they are connected to ablood treatment unit 76 of a blood treatment machine. The bloodtreatment unit can be for instance formed by a casing housing asemipermeable membrane separating a blood chamber and a treatment fluidchamber. The blood chamber of unit 76 is connected with the arterial andvenous line ends 72 and 75.

The treatment fluid chamber is connected in use with an outlet line 77,for the spent treatment liquid, and with an inlet line 78, for the freshtreatment liquid (prepared by the blood treatment machine or coming fromappropriate containers. Of course in case of treatments where no freshliquid is required, then the treatment fluid chamber is only connectedwith outlet line 77.

Depending upon the blood treatment to be performed the blood circuit canbe connected to corresponding connectors leading to a blood chamber of adialyzer, of a hemofilter, of a plasmafilter, of an ultrafilter, of anhemodiafilter or of other treatment unit.

During treatment or during other procedures (such as priming or rinsing)liquid is pumped into the first blood chamber via the tube 79, thechannel 14 directs the liquid towards the air separator top wall andprovides for a uniform speed reduction in the flow as the channel isrelatively long as compared to the chamber vertical and relatively widein correspondence of the orifice. Therefore the liquid leaves thechannel in a position which is sufficiently distant from the outletport; moreover the direction of the flow, the speed reduction anduniform flow allow for a very efficient de-bubbling with no foamcreation and minimal perturbations in correspondence of the air-bloodinterface (see FIG. 7B). Significant is the comparison of FIGS. 7A and7B wherein one can easily see how the air separator of the inventionprovides for significant reduction in the perturbation and for a morestable liquid level. Moreover the distance of the orifice 15 from theoutlet port 11, the geometry of the first channel and of the firstchamber, and the specific position of the filter give as a result thatthe filter surface does not present areas of stagnation, therebyreducing the risk of clotting or of trapping bubbles. FIGS. 8A and 8Bemphasize the improvement offered by the present invention as the entirefilter 19 surface is touched by fluid having a certain sufficiently highspeed. By contrast the filter of the prior art chamber of FIG. 8Apresents a top region of fluid stagnation.

1-42. (canceled)
 43. Air separator for extracorporeal fluid treatmentsets comprising: a first chamber where fluid can be received, the firstchamber presenting: a bottom wall, a top wall, a lateral wall extendingbetween the top and bottom walls, an inlet port and an outlet portassociated to the bottom wall and in fluid communication with the firstchamber, a first channel extending along at least a portion of thelateral wall and having a first end, connected to the inlet port, and asecond end terminating in an orifice which is closer to said top wallthan to said bottom wall.
 44. Air separator according to claim 43,wherein said first channel has a first portion extending from the firstend and at least a second portion terminating in correspondence of thesecond end, the second portion presenting a flow passage cross sectiongreater then that of the first portion.
 45. Air separator according toclaim 44, wherein at least the second portion has a continuously andprogressively increasing flow passage cross section.
 46. Air separatoraccording to claim 44, wherein the flow passage cross section of thefirst portion and the flow passage cross section of the second portionare substantially constant.
 47. Air separator according to claim 46,wherein said first channel comprises a connection portion extendingbetween the second portion and the first portion.
 48. Air separatoraccording to claim 47, wherein the connection portion has aprogressively increasing flow passage cross section.
 49. Air separatoraccording to claim 47, wherein the connection portion comprises at leastone aperture that puts into communication the first channel directlywith the first chamber.
 50. Air separator according to claim 43, whereinthe first portion and the second portion extend in correspondence of andsubstantially parallel to the lateral wall of the first chamber.
 51. Airseparator according to claim 43, wherein the first portion is longerthan the second portion.
 52. Air separator according to claim 43,wherein the orifice opens into the first chamber and faces said topwall.
 53. Air separator according to claim 52, wherein said orificeextends on a plane perpendicular to the lateral wall of the firstchamber.
 54. Air separator according to claim 44, wherein a ratio A1/A3is comprised between 1.5 and 2.5, where: A1 represents the measure ofthe flow passage cross section area of the first channel incorrespondence of said orifice, A3 represents the measure of the flowpassage cross section area of the first channel in correspondence of thefirst portion.
 55. Air separator according to claim 43 wherein a ratioD2/D1 is greater than 0.5 and for instance comprised between 0.55 and0.70, where: D1 represents the measure of the distance between top wallinner surface of the first chamber and bottom wall inner surface of thefirst chamber, D2 represents the measure of the distance between thehorizontal plane where the orifice of the first channel extends and thebottom wall inner surface of the first chamber.
 56. Air separatoraccording to claim 43, wherein ratio A1/A2 is greater than 0.25 and lessthan 0.75, where: A1 represents the measure of the flow passage crosssection area of the first channel in correspondence of said orifice, A2represents the measure of the flow passage cross section area of thefirst chamber in correspondence of a section horizontally aligned withthe orifice.
 57. Air separator according to claim 43, comprising afilter engaged to the bottom wall in correspondence of the outlet port.58. Air separator according to claim 57, wherein the filter axiallyextends into the first chamber according to a direction substantiallyparallel to the first channel, this latter being parallel to lateralwall.
 59. Air separator according to claim 58, wherein the filterpresents an overall axial extension substantially not greater than 70%of the measure of the distance between the horizontal plane where theorifice of the first channel extends and the bottom wall inner surfaceof the first chamber.
 60. Air separator according to claim 59, whereinthe filter has an axial extension not greater that that of the firstportion of said first channel.
 61. Air separator according to claim 43,wherein the first channel and the first chamber are made in one singleplastic piece.
 62. Air separator according to claim 43, wherein the airseparator has a flattened structure, said first channel and said firstchamber having a substantially square shaped transverse section.
 63. Airseparator according to claim 43, wherein said lateral wall presents: afront wall, a rear wall spaced from the front wall, and side wallsextending between said front and rear walls, said air separatorcomprising an intermediate wall extending between the front and realwalls and laterally delimiting said channel in cooperation with one ofsaid side walls.
 64. Air separator according to claim 63, wherein saidintermediate wall presents a first wall portion parallel to said oneside wall, a second wall portion parallel to the same side wall and adeflecting portion connecting said first and second portion therebyforming said first portion, said connection portion and said secondportion.
 65. Air separator according to claim 43 comprising: a secondchamber positioned in side by side relationship with respect to saidfirst chamber, said second chamber being delimited by respective bottomwall, top wall, and lateral wall extending between the top and bottomwalls, and being provided with respective inlet and outlet ports. 66.Air separator according to claim 65, wherein said lateral wall of thesecond chamber presents: a front wall, a rear wall spaced from the frontwall, and side walls extending between said front and rear walls, saidfirst and second chamber being in one single piece and sharing a commonside wall which extends in correspondence of a central zone of the airseparator.
 67. Air separator according to claim 66, comprising a secondchannel extending parallel to the lateral wall of the second chamber andhaving a first end, connected to the inlet port, and a second endterminating into the second chamber, the second channel having constantcross section and presenting a deflector in correspondence of its secondend defining an orifice facing the lateral wall of the second chamber.68. Air separator according to claim 67, wherein the orifice of thesecond channel is substantially at the same height as the orifice of thefirst channel.
 69. Air separator according to claim 43, wherein thelateral wall of said first chamber comprises pressure transducer meansand wherein said first channel ends immediately below said pressuretransducer means.
 70. Air separator according to claim 69, wherein thelateral wall of said second chamber comprises pressure transducer meansand wherein said second channel ends immediately below said pressuretransducer means.
 71. Air separator for extracorporeal fluid treatmentsets comprising: a first chamber where fluid air can be received, thefirst chamber presenting: a bottom wall, a top wall, a lateral wallextending between the top and bottom walls, an inlet and an outlet portassociated to the bottom wall and in fluid communication with the firstchamber, a first channel having a first end, connected to the inletport, and a second end terminating into the first chamber, a filterengaged to the bottom wall in correspondence of the outlet port andaxially extending into the first chamber according to a directionsubstantially parallel to the first channel, the filter presenting anoverall axial extension which is not greater than 70% of the overalllongitudinal extension of the first channel.
 72. Air separator accordingto claim 71, wherein said first channel has a first portion extendingfrom the first end and at least a second portion terminating incorrespondence of the second end, the first portion presenting a flowpassage cross section greater then that of the second portion.
 73. Airseparator according to claim 72, wherein the first portion and thesecond portion extend in correspondence of and substantially parallel tothe lateral wall of the first chamber, the flow passage cross section ofthe first portion and the flow passage cross section of the secondportion being substantially constant.
 74. Air separator according toclaim 72, wherein the first portion is longer than the second portionand longer than the filter axial extension.
 75. Air separator accordingto claim 72, wherein the second end of said first channel forms anorifice, which opens into the first chamber and extends on a planeperpendicular to the lateral wall of the first chamber.
 76. Airseparator according to claim 75, wherein a ratio A1/A3 is comprisedbetween 1.5 and 2.5, where: A1 represents the measure of the flowpassage cross section area of the first channel in correspondence ofsaid orifice, A3 represents the measure of the flow passage crosssection area of the first channel in correspondence of the firstportion.
 77. Air separator according to claim 75, wherein a ratio D2/D1is greater than 0.5 and for instance comprised between 0.55 and 0.70,where: D1 represents the measure of the distance between top wall innersurface of the first chamber and bottom wall inner surface of the firstchamber, D2 represents the measure of the distance between thehorizontal plane where the orifice of the first channel extends and thebottom wall inner surface of the first chamber.
 78. Air separatoraccording to claim 75, wherein ratio A1/A2 is greater than 0.25 and lessthan 0.75, where: A1 represents the measure of the flow passage crosssection area of the first channel in correspondence of said orifice, A2represents the measure of the flow passage cross section area of thefirst chamber in correspondence of a section horizontally aligned withthe orifice.
 79. Air separator for extracorporeal fluid treatment setscomprising: a first chamber where fluid can be received, the firstchamber presenting: a bottom wall, a top wall, a lateral wall extendingbetween the top and bottom walls, an inlet and an outlet port associatedto the bottom wall and in fluid communication with the first chamber, afirst channel having a first portion connected to the inlet port, and asecond portion terminating into an orifice, wherein the flow passagecross section of the first portion and the flow passage cross section ofthe second portion are substantially constant and the first portion flowpassage cross section is greater then that of the second portion. 80.Air separator according to claim 79, wherein ratio A1/A2 is greater than0.25 and less than 0.75, where: A1 represents the measure of the flowpassage cross section area of the first channel in correspondence ofsaid orifice, A2 represents the measure of the flow passage crosssection area of the first chamber in correspondence of a sectionhorizontally aligned with the orifice.
 81. Air separator according toclaim 79, wherein a ratio D2/D1 is greater than 0.5 and for instancecomprised between 0.55 and 0.70, where: D1 represents the measure of thedistance between top wall inner surface of the first chamber and bottomwall inner surface of the first chamber, D2 represents the measure ofthe distance between the horizontal plane where the orifice of the firstchannel extends and the bottom wall inner surface of the first chamber.82. Air separator according to claim 79, wherein ratio A1/A2 is greaterthan 0.25 and less than 0.75, where: A1 represents the measure of theflow passage cross section area of the first channel in correspondenceof said orifice, A2 represents the measure of the flow passage crosssection area of the first chamber in correspondence of a section alignedwith the orifice.
 83. Air separator according to claim 43, comprising atleast one selected in the group including: a venous line which has atleast one end designed to be connected to a patient and another enddesigned to be connected with a blood treatment unit, said venous lineincluding a first flexible tube engaged to the inlet port of the firstchamber, a second flexible tube engaged to the outlet port of the firstchamber, an arterial line which as at least one end designed to beconnected to a patient and another end designed to be connected with ablood treatment unit, said arterial line including a third flexible tubeengaged to the inlet port of the second chamber, and a fourth flexibletube engaged to the outlet port of the second chamber and to one wall ofsaid second chamber for forming a loop which is symmetric about a loopaxis transverse to the lateral wall of the second chamber.
 84. Bloodtreatment machine comprising: a dialysis liquid preparation module forpreparing dialysis liquid, at least a waste line for receiving spentdialysate, a blood treatment unit having a first chamber connected todialysis liquid preparation module and to the waste line, and a secondchamber separated from the first chamber by means of a semipermeablemembrane, and the air separator of claim 83, wherein the arterial lineis connected an inlet of the second chamber and the venous line isconnected to an outlet of the second chamber.